Reply to the comment of Ana I. Alvarez and Gracia Merino regarding “Assessment of ABCG2-mediated transport of xenobiotics across the blood-milk barrier of dairy animals using a new MDCKII in vitro model” by Wassermann et al. 2013

Abstract

June 2009) and GQ141082 (oABCG2: submitted on 3 July 2009). These generated ABCG2 full-length clones consist of the open reading frame (ORF) sequence as well as an 5′ untranslated region (5′-UTR) where regulatory elements are located. In this context, we identified besides other reg-ulatory elements such as SP-1 and AP-1 aryl hydrocarbon receptor response elements (AhRE) in the bovine as well as the caprine ABCG2 5′-UTR (Wassermann et2013 al. ). In further mechanistic studies, we showed that the func-tional expression of ABCG2 was induced due to binding of ligand-activated AhR to AhRE sequences in the ABCG2 5′-UTR (Halwachs et2012). Merino and coworkers al. (Merino et al. 2009) as well as Real and coworkers (Real et al. 2011) did not provide NCBI accession numbers for the hepatocellular ABCG2 cDNA sequences in their pub-lications. To our knowledge, the NCBI database entry (NM_001037478) from Real et al. was first published and accessible in June 2012. Since then, it was not possible to perform sequence analysis to determine cDNA sequence homology between the bovine hepatocellular and mam-mary ABCG2 clones. In addition, we did not only gener-ate a full-length bovine mammary ABCG2 cDNA sequence but also caprine and ovine mammary ABCG2 sequences. In this context, differences between the three species occurred regarding the ABCG2 cDNA as well as protein sequences (Wassermann etal. 2013 ). Former studies (Wassermann et al. 2013) as well as the present publication additionally revealed species-dependent differences regarding the sub-strate specificity of the generated MDCKII-ABCG2 cell lines. However, the aim of our research was to generate tis-sue-specific full-length ABCG2 cDNA clones to investigate the influence of xenobiotics on the tissue-specific expres-sion of ABCG2. In this context, the generated MDCKII cell lines stably expressing bABCG2, cABCG2 or oABCG2 represent a new in vitro model.